The Olympics come and go, but true sporting rivalries last forever – usually as a proxy for deeper issues. Spain's two most famous institutions, the football clubs Real Madrid and Barcelona, have been representing the centre and fringes of the nation since the Civil War. That Real was founded by Catalans and Barça by foreign merchants has long been forgotten: Franco supposedly favoured Real, while Barcelona represented Catalan resistance.

Today, surveys show that support for the two teams (and all Spaniards take sides on the issue – the author has talked to everyone, from refs to chefs, hacks to centre backs) splits pretty firmly along left-right lines. Myth has replaced reality.

Even the teams' sporting philosophies are opposed. Real signs proven talent and global superstars; Barcelona raises its own. Richard Fitzpatrick suggests that Barça's youth academy, La Masia, is the most respected Spanish educational establishment since Salamanca University was knocking 'em dead in the Middle Ages.

These are great times for both clubs. The world's best and maybe best-loved player, Lionel Messi, stars for Barcelona, much to the annoyance of the world's second best player, Real's punchable but brilliant Cristiano Ronaldo. While the monkish Pep Guardiola recently resigned, Madrid's manager, football's pantomime villain José Mourinho, continues to dominate the partisan Spanish sports press.

Spanish fan culture is very different from Britain's. Away support is non-existent. Sadly, disconcerting opponents with racist abuse is considered acceptable. The worst, though, is saved for those who switch clubs. Luis Figo, who played at the Camp Nou in front of 100,000 haters, treasures the uniqueness of the experience.

Glasgow's great rivalry is currently suspended: Rangers are bankrupt and demoted, and doomsayers predict meltdown for the Scottish game. For all Barcelona's separatist posturing, Catalan independence would mean St Jordi's team have no dragon to slay. As this intriguing, occasionally tortuous book explains, these greedy giants need each other more than they can dare admit.